Custom shaped free-standing nano structures and microstructures have many uses, for example, as support particles in combinatorial chemistry and as labels for molecules. Known methods of creating custom shaped micro particles are described in GB 2306484 and WO 00/16893.
In GB 2306484, a method is described of making solid support particles marked with a machine readable code, for use in combinatorial chemistry techniques. The particles are made using deposition, etching and lift-off techniques similar to those used to make micro electronic integrated circuits and micro electromechanical systems (MEMS). A silicon wafer substrate is coated firstly with a soluble sacrificial layer, then with a layer from which the particles will be made, finally with a layer of photosensitive polymer resist. The layer of photosensitive polymer resist is exposed to ultraviolet light through a photolithographic mask which defines the particle shapes. The particles are created by removing unexposed resist and etching away the revealed areas of material around the particles. The particles may then be freed from the silicon wafer substrate by dissolving the sacrificial layer which underlies the particles. The particles may be patterned with text, holes, grooves or notches. This creates a code, which is readable optically to identify each particle. The particles are sized with a longest dimension of between 1 and 500 microns.
In WO 00/16893, a method of making micro-barcode labels is described. The labels are made by standard optical lithography and dry etching, and the barcode is stored as a series of holes in the micro labels. The labels are made of aluminium and are anodised to allow the attachment of a wide range of biochemically active agents for use as highly selective probes. Each micro label is typically of a size of about 100 microns long by 10 microns wide by 1 micron thick.
Although both of the above methods allow small free standing structures to be fabricated, they both suffer from the problem that they require rather complicated and time consuming fabrication techniques.